1. Field of the Invention
The present invention relates to the field of power supplies, and more particularly to multiphase switching power supplies.
2. Description of the Related Art
Power supplies are used in various types of devices. There are many specialized types of power supply circuits with various advantages and disadvantages. Microprocessors in computers may require a power supply circuit that regulates a high level of current while maintaining a high level of efficiency.
One such type of specialized power supply circuit is a switching regulator. Switching regulators typically provide an output with a lower voltage than the unregulated input while at the same time providing an output with a higher current than the current drawn from the unregulated supply. This is accomplished by a passive transistor that is constantly switching between the saturation mode and the nonconducting mode. Because the passive transistor is either in saturation or not conducting, there is very low power dissipation. A switching regulator therefore can regulate a high amount of current at a high efficiency rate.
A disadvantage with switching regulators is known as the "ripple effect." The ripple effect refers to ripples that are periodic variations in the output voltage that have to be smoothed out in order to generate a genuine DC current. The ripple effect problem may be reduced or eliminated by coupling multiple switching regulators in parallel and operating them such that they are out of phase with respect to one another. This configuration is known as a multiphase switching regulator. A multiphase switching regulator typically produces a high current output with high efficiency while at the same time reducing ripple. Consequently, a multiphase switching regulator is a popular choice for use in a power supply circuit where high levels of current and efficiency are desired.
Many microprocessors are configured to selectively operate in a low power mode of operation. During low power mode, the microprocessor may be configured to power down certain functional blocks (e.g. those that are inactive) and/or reduce the frequency of its internal clock(s). Powering down certain portions of the microprocessor and/or reducing clocking frequencies may advantageously reduce power consumption. When the microprocessor returns to a normal mode of operation, the microprocessor draws relatively higher amounts of current.
Unfortunately, when the microprocessor is operating in low power mode, a multiphase switching regulator becomes more inefficient as a percentage of the total current generated. This is because the transistors in the switching regulators continue to switch at the same frequency as during the normal mode of operation. Since the transistors are switching at the same frequency, the capacitive losses associated with the switching are the same during the low power and normal modes of operation. However, since less current is drawn during the low power mode of operation, the switching becomes more inefficient as a percentage of the total current generated. Therefore, an improved multiphase power supply circuit is desired that will lower switching-related power losses during low power modes of operation.